When building, if images are being pushed, ensure that only
named images (i.e. services with a populated `image` field)
are attempted to be pushed.
Services without `image` get an auto-generated name, which
will be a "Docker library" reference since they're in the
format `$project-$service`, which is implicitly the same as
`docker.io/library/$project-$service`. A push for that is
never desirable / will always fail.
The key here is that we cannot overwrite the `<svc>.image`
field when doing builds, as we need to be able to check for
its presence to determine whether a push makes sense.
Fixes#10813.
Signed-off-by: Milas Bowman <milas.bowman@docker.com>
Milas Bowman
Benjamín Guzmán